The vanadium-based halide double perovskites Rb2NaVCl6 and K2NaVCl6 are studied systematically in terms of various physical aspects like structural, mechanical, thermodynamic, electronic, thermoelectric performance and optical efficiency. The studied compounds crystallize in a face-centered cubic structure (space group#225, Formula: see text) with lattice constants of 10.41 Å and 10.36 Å, respectively. Structural, mechanical and dynamical stability was confirmed through Goldschmidt tolerance factors, Born–Haun criteria and phonon dispersion spectra. Mechanical analysis indicates ductile behavior in Rb2NaVCl6 and brittleness in K2NaVCl6, with both exhibiting positive Cauchy pressures and notable incompressibility and stiffness. Direct electronic band gaps of 2.86 eV (Rb2NaVCl6) and 2.81Formula: see texteV (K2NaVCl6) were observed. Optical studies revealed significant absorption (Formula: see textFormula: see textcmFormula: see text in the visible range and static refractive indices above 1.6. Thermoelectric performance was promising, with high Seebeck coefficients (Formula: see text150–250Formula: see text Formula: see textV/K), power factors over Formula: see textFormula: see textW/mK 2 s and figure-of-merit (ZT) values approaching 1.47 at room temperature. These findings suggest that Rb2NaVCl6 and K2NaVCl6 are stable, eco-friendly, and efficient to be used for optoelectronic and thermoelectric industrial applications.
Asif et al. (Fri,) studied this question.